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Loma Prieta Earthquake, October 18, 1989, Part 2

On October 17, 1989, a 7.1 magnitude earthquake occurred near Loma Prieta in the Santa
Cruz Mountains. This earthquake is also known as the "San Francisco World Series Earthquake."
The slide set focuses on the effects in San Francisco and Oakland. It highlights the
damage in the Marina area of San Francisco. The set also includes photographs in the
area south of Market Street where five deaths occurred, the San Francisco-Oakland
Bay Bridge, and the Nimitz Freeway (I-880) where 41 deaths occurred. Movement occurred
along a 40-km segment of the San Andreas fault from southwest of Los Gatos to north
of San Juan Bautista. Measurements along the surface of the Earth after the earthquake
show that the Pacific plate moved 1.9 m to the northwest and 1.3 m upward over the
North American plate. The upward motion resulted from deformation of the plate boundary
at the bend in the San Andreas fault. At the surface the fault motion was evident
as a complex series of cracks and fractures. Even though the earthquake occurred in
the remote Santa Cruz Mountains, it caused severe damage in San Francisco and Oakland
80 km to the north. This is somewhat unusual for an earthquake of this magnitude.
Some of the statistical results of the disaster were: more than $7 billion in property
damage (2.5 billion in San Francisco alone), 414 single-family homes destroyed, 104
mobile homes destroyed, 18,306 homes damaged, 97 businesses and 3 public buildings
destroyed, 2,575 businesses damaged, 12,000 people displaced from homes and housed
in shelters, 3,757 injuries, and 67 deaths. One of the areas in San Francisco that
sustained major damage was the Marina District. This area was a lagoon at the time
of the 1906 San Francisco earthquake. During that earthquake the margins of the lagoon
shook violently.However, after the 1906 earthquake, the lagoon was filled with sand
and rubble of destroyed buildings to make a fairground for the 1915 Panama-Pacific
International Exposition. This fill area later became the site of an expensive real-estate
development known as the Marina District. The unconsolidated soils amplified the shaking
and became liquefied (behaved like a dense fluid) causing permanent deformation of
the ground. This was one of the causes of the increased damage in the area. Construction
practices also contributed to the damage. Some four-story buildings built above garages
had inadequate lateral bracing. Thirty-five of the buildings in the Marina District
were eventually torn down and 150 others were structurally damaged. The two major
causes of structural failures were poor soil conditions and inadequate structural
design. South of Market Street, several buildings between 5 and 10 stories high were
damaged. Old masonry buildings were badly damaged, including a warehouse where collapse
of fourth floor exterior walls killed five people parked in cars along the street.
There were also severely damaged buildings in the Mission District. In Oakland, severe
damage occurred to several mid-rise buildings and many old brick buildings in the
downtown area. Primarily due to the effects of liquefaction, buried underground utilities
such as gas pipelines, water lines, and sewer lines were heavily damaged. This left
about one thousand homes without gas or water. As in the 1906 earthquake, fires in
the Marina District could not be fought with city water because water mains had failed.One
of the sources for concern produced by the earthquake is the damage or failure of
transportation systems at comparatively large distances from the epicenter. The most
deadly structural failure of the earthquake occurred when the upper deck of the Interstate
880 (Nimitz Freeway) in Oakland fell onto the lower roadway causing an official death
toll of 41. Another spectacular failure occurred on the Oakland Bay Bridge. Interstate
280, the Embarcadero Freeway, and Highway 101 at Fell Street were also damaged. In
Oakland, Highway 980 and the MacArthur Maze developed cracks in the support columns.
It will cost about $1.5 billion to rebuild state and local roads damaged in the earthquake.
In addition to damage to roads, the Oakland International Airport, naval port, and
the Alameda Naval Air Station runways were damaged by liquefaction. It is interesting
to compare this earthquake with the slightly smaller (magnitude 6.9) Armenian earthquake
of December 1988 that killed 25,000 people and destroyed entire towns. Good construction
and engineering practices in the Loma Prieta area obviously contributed to the preservation
of property and human lives.